class: center, middle, inverse, title-slide # CRS & Projections: How to choose a CRS --- layout: true <div class="dk-footer"> <span> <a href="https://rfortherestofus.com/" target="_blank">R for the Rest of Us </a> </span> </div> --- class: center, middle, dk-section-title, contain background-image:url("images/impossible-shapes.png") background-size: 80% # CRS & Projections: How to choose a CRS ??? --- class: middle, contain .pull-left[ <br> This video gets into the technical details of finding a **suitable** projected CRS. This is only a concern for geocomputations and GIS analysis - for straightforward mapping you can use our magic CRS - 4326. ] .pull-right[ <img src='images/stop-shield-traffic-sign-road-sign-39080.jpeg'/> ] ??? --- ## There are no all-purpose CRS > “There exist no all-purpose projections, all involve distortion when far from the center of the specified frame” (Bivand, Pebesma, and Gómez-Rubio 2013) ??? --- ## National Mapping Agencies to the rescue If your data lie within country borders then you can take advantage of CRS specifically designed by *National Mapping Agencies*. These agencies create nation-level CRS that allow precision... - ... national infrastructe planning. - ... cellular network coverage. - ... coastal erosion monitoring. - ... weather forecasting. - ... maps for civilian, government and military uses. ??? --- ### Governments usually supply data in national CRS GIS datasets obtained from government data portals are usually provided in the national CRS - for instance [geoportal.statistics.gov.uk](https://geoportal.statistics.gov.uk/datasets/local-authority-districts-may-2020-boundaries-uk-bfe). We can then use `st_crs()` and `st_transform()` to project other datasets into the national CRS. ```r national_gis_dataset <- read_sf("data/shapefiles") your_own_data <- read_sf("data/points") your_own_data %>% st_transform(st_crs(national_gis_dataset)) ``` ??? --- ## RSTUDIO CODING SLIDE ??? --- ### Hunting for national CRS There isn't a perfect process for finding national CRS and many countries just don't have one. The first place I recommend searching is [EPSG.io](https://epsg.io) ??? --- class: inverse, center, middle ## When National CRS won't cut it --- ## Oceanographic CRS .pull-left[ There are Oceanographic CRS for entire oceans and small regions. Small region oceanographic CRS are usually designed for oil exploration/extraction. I recommend using [EPSG.io](https://epsg.io) to search for appropriage CRS for your data.] .pull-right[ <img src='images/pexels-photo-1001682.jpeg'/> ] ??? --- ## Projection Wizard [projectionwizard.org](https://projectionwizard.org/) is a free interactive tool for creating custom CRS. <center><img src='images/projection-wizard.png' height='300px'/></center> ... but to use it you need to decide what type of projected CRS you need. --- ## Projected CRS Types <center><img src='images/projected-crs-types.png' height='400px'/></center> Source: [ihatecoordinatesystems.com/](https://ihatecoordinatesystems.com/) --- ## RStudio Coding Slide